What is the ruling on someone who stated in the health insurance application that they had no previous illnesses, while they knew they had an illness beforehand, this being necessary for obtaining residency? And is it sufficient to donate the value of the previous health allowance for a year and a half as a solution to the issue?

You erred by concealing your illness, for this is a forbidden lie. You must adhere to the insurance conditions, for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." It is not permissible to deceive or cheat to obtain treatment for a pre-existing condition that the insurance did not approve for treatment, whether the insurance is cooperative or commercial. Note that commercial insurance is fundamentally impermissible to subscribe to.

Therefore, you are not permitted to seek treatment for the pre-existing condition at the expense of the insurance. You must return the money spent on your treatment to its rightful owners if they can be identified; donating it is not sufficient. However, if the insurance was commercial, you may benefit from what you paid to them. If the cost of treatment does not exceed what you paid, then there is nothing against you. Nevertheless, you must discontinue the insurance and repent to Allah for the deception, cheating, and the forbidden transaction.